One of the biggest debates in archaeology is what destroyed the extensive, highly-advanced Maya civilization 1,000 years ago. It's known that the empire went through a long collapse from roughly 800 to 1,000, leaving behind a network of pyramids and monumental architecture in the Yucatán jungles. But why? We have only educated guesses, and one of the most widely-believed theories is that some kind of climate catastrophe drove the Maya to abandon their cities in droves.

Now, two Earth scientists have carefully analyzed rock samples from the Yucatán, which revealed water levels in local lakes, as well as chemical traces that show likely rainfall over the decades of the collapse. What the scientists found was more evidence that the region suffered from drought during the typically rainy summers — but the drought was fairly mild. There were probably fewer hurricanes in the ocean driving rainstorms to land. In a paper published today in Science, researchers Martín Medina-Elizalde and Eelco J. Rohling call it "a succession of extended drought periods interrupted by brief recoveries."

Is it really possible that a mild drought, no matter how many centuries it lasted, could really topple an empire? After all, civilizations in Europe have endured everything from plagues to the Little Ice Age, and people did not abandon the cities.

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Medina-Elizalde and Rohling suggest:

If these repeated episodes of drier climate had a significant role in the fate of the Classic Maya civilization, as suggested by archaeological evidence, then this would imply that the ecological carrying capacity of the Yucatán Peninsula is highly sensitive to precipitation reductions.

In other words, it's possible that it didn't take much of a drought to usher in a catastrophic series of crop losses or other environmental problems. And these problems, in turn, could foment dramatic social upheavals.

The scientists note that this does not bode well for the future of the region, since in coming decades the Yucatán Peninsula is likely to experience "modest reductions in precipitation" like those during the collapse of the Maya civilization.

Ultimately, we have to consider the possibility that it wasn't simply a mild drought that destroyed the Empire, but that the Empire also destroyed itself the way many great European and Asian powers have — by waging war until their resources were depleted and no willing soldiers were left. The Maya probably weren't just passive victims of climate change. They were a powerful polity, spread out across huge swathes of the Yucatán. They had advanced agricultural techniques, and new LiDAR studies of regions around Maya center Caracol reveal that they remolded much of the land in the area to make way for farms, roads, and homes. Given their technological sophistication, it's possible that the Maya might have survived the drought if it hadn't been for war taxing their resources. In other words, the Mayan Empire's demise may have resulted from a mix of social and environmental factors, and would have been far more complex than mere food shortages due to drought.